Canine visceral leishmaniasis (CVL) is an important emerging zoonosis in countries around the Mediterranean basin, in the Middle East, and in Latin America (20). This severe disease is caused by Leishmania infantum in the Mediterranean area, Middle-East and Asian countries and L. chagasi in Latin America (20, 21). Due to their genotypic relationships, both species causing CVL in different continent can be considered identical (26).
Upon infection dogs can develop different forms of the disease; asymptomatic, oligosymptomatic or symptomatic (4). Symptomatic infection results in death and its clinical manifestations include cutaneous alterations like alopecia, dermatitis, onychogryphosis (3, 11), and also visceral manifestations with renal, hepatic and cerebral alterations (18, 28). Some of the infected dogs remain asymptomatic or develop few mild symptoms and are classified as oligosymptomatic (4). CVL can not be considered only as a veterinary disease since infected dogs (even asymptomatic ones) are the main domestic reservoir of the parasite for human infection (1). Thus, to reduce the transmission of Leishmania from dogs to humans it is necessary to diagnose canine leishmaniasis as early as possible.
The presence of anti-Leishmania specific antibodies in asymptomatic, oligosymptomatic and symptomatic infected dogs (4, 9, 34) has allowed the development of serologic tests including immunofluorescent antibody test (IFAT), western blot, immunochromatographic test, and enzyme-linked immunosorbent assay (ELISA) (reviewed in (23)). Diagnosis of CVL using ELISA assays based on crude soluble Leishmania antigens (SLA) have shown to have high sensitivity but low specificity because of antigenic relatedness between Leishmania and other pathogenic protozoa (16). As a strategy to develop specific serodiagnostic test for CVL, different parasite antigens were obtained as recombinant proteins (5, 10, 24). However, due to the high variability observed in the humoral response of individual infected dogs against different parasite antigens (19, 31), efficient diagnosis based on recombinant proteins may require a mixture of recombinant proteins or the use of chimerical proteins containing several non-related parasite antigens (6, 31, 36). Specific diagnosis of CVL can be also developed using crude parasite fractions analyzed by western blotting or preparations purified from the parasite (8, 17). For example, an ELISA assay based on soluble Leishmania antigen (SLA) has already been developed (27, 31). However, this SLA-based assay is not enough specific for diagnosing asymptomatic Leishmaniasis. In addition, the sera from subjects having other parasite diseases distinct from Leishmaniasis will give false positive reaction with a SLA-based assay. Therefore, there is still a need for an improved diagnostic method of a parasitic disease such as Leishmaniasis, which does not have all the drawbacks of existing methods.